Miniaturized stacked switch assembly



Jan. 16, 1968 E. s. ARLIN MINIATURIZED STACKED SWITCH ASSEMBLY Filed Aug. 19, 1966 um m E V W EDWARD S. ARLIN United States Patent Office 3,364,323 Patented Jan. 16, 1968 3,364,323 MINIATURIZED STACKED SWITCH ASSEMBLY Edward S. Allin, Norwalk Township, Ohio, assigner to Norwalk Thermostat Company, Norwalk, Uhio, a corporation of @hie Filed Aug. 19, 1966, Ser. No. 573,655 5 Claims. (Cl. 20G- 138) This invention relates to electrical switches and more particularly to means for reducing the size of such switches While maintaining the required degree of electrical isolation between conductive elements thereof.

Safety codes and standards have been adopted by industry to define minimum insulation requirements for certain equipment applications. For example, the American Standard Listing Requirements for Automatic Burner Ignition and Safety Shutofr- Devices issued -by the American Gas Association, Inc. requires a minimum over surface spacing between any uninsulated live metal part and an insulated live-metal part of opposite polarity, an uninsulated grounded dead-metal part other than the enclosure, or an exposed dead-metal part which is isolated (insulated) of lt inch for -l50 Volts, 3/8 inch for 151- 300 volts and -1/2 inch vfor 301-600 volts. In the form of switching device employing a stack of insulating bushings, contact blades and terminals assembled on a conductive post such as a rivet, these requirements have been met by employing the annular face of an insulating bushing having a thickness of the requisite dimension. The Wall thereby spaced the column from the blades and terminals by embracing the post `and maintaining apertures in the blades and terminal coaxial with the post and spaced therefrom radially by the wall thickness. Constructions of this type are typied by P. R. Lee Patent 2,689,897 of Sept. 21, 1954.

The type of assembly described has in the past imposed restrictions on the size of the elements and thus of the assemblies which have precluded their utilization where insufficient space is available. Thus many home appliance applications have required more expensive electrical switches.

It is an object of this invention to reduce the size of electrical switches of the type described while satisfying the electrical insulation requirements for such switches.

More particularly an object of this invention is to improve the insulating bushings employed in switches of the type described.

These objects are achieved in accordance with one feature of this invention by reducing the radial spacing re- Y quired between a conductive post and the perimeter of the apertures in those conductive elements stacked upon the column to less than the requisite over surface minimum spacing. This is achieved by interposing between successive `conductive elements in the stack insulating bushings which provide a portion of the spacing along a collar forming a cylindrical surface coaxial with and longitudinal of the post and a portion of the spacing radial of the post across the wall thickness of the coll-ar on the bushing. This spacing is achieved by employing insulating bushings in the stack which have a secondary cylindrical cavity or counterbore complementary to the collar so that the collar is telescoped within the cavity of an adjacent bushing when the stack is assembled. The collar and cavity are coaxial with a primary axial cylindrical cavity through which the conductive post extends. They are proportioned so that the difference in radius between the counterbore 0r collar and the primary cavity is less than the minimum over surface spacing required for the switch. The depth of the counterbore or height of the collar is at least equal to the minimum over surface spacing less the radial difference. Thus, the minimum over surface spacing between the post and any ring shaped conductive elements mounted on the bushing collar is made up of the wall thickness of the collar which is less than the requisite spacing, and a wall length from the face of the conductive element mounted on the collar to the outermost limit of the collar.

Since the radial differences utilized in the described stack are less than the minimum over surface. spacings, the conductive elements mounted thereon can be narrower than heretofore for a given rating and the switch stack can be smaller.

The above and additional objects and features will be more fully appreciated from the following detailed description when read with reference to the accompanying drawing in which:

FIG. 1 is a sectioned elevation of a switch stack constructed according to this invention;

FIG. 2 is a perspective of one form of insulating bushing according to this invention with portions broken away to reveal its structure; and

FIG. 3 is a perspective with portions broken away of a second form of insulating bushing which cooperates with the bushing o-f FIG. 2.

FIG. l illustrates in general form a conventional thermostat embodying this invention. It comprises a mounting screw 11 and a nut 12 utilized for mounting a stacked assembly of terminals, contact blades and actuating elements. The thermostatic switch utilized for illustrative purposes is assembled on a post or rivet 13 and comprises a bi-metallic blade 14 having an insulating pin 15 at its end remote from the stack, a thermostatically actuated resilient blade 16 having a contact 17 and a cooperating contaet 18 mounted on a resilient blade 19. An electrical circuit is provided through the switch from terminal 21 to blade 16 through contacts 17 and 18 to blade 19 and its terminal 22. Manual adjustment of the position of blade 16 is afforded through a pin 23 abutting the upper surface of the blade as viewed in FIG. 1 and supported in a bushing 24 which is staked or otherwise suitably secured in a rigid support blade 25. The bushing 24 is internally threaded and has a push screw 26 mechanically coupled to the pin 23 whereby the rotation of the screw adjusts the position of pin 23 and the position of blade 16.

Each of blades 14, 19, 16 and 25 and terminals 21 and 22 are maintained in stacked relationship. Blade 14 is provided with a circular aperture 27 closely fitting the outer diameter of circular rivet 13 and is fitted thereover to abut against the lower head 28 of rivet 13. Blade` 19 and its electrically coupled terminal 22 are mounted in abutting relationship on collar 29 of bushing 31 -by means of apertures 32 and 33 respectively which are circular in form and closely fit the outer diameter of the circular collar 29. Bushing 31 in turn has an axial bore 34 the walls of which fit and extend along a portion of the length of post or rivet 13.

Terminal 22 and blade 19 are isolated from blade 14 by bushing 35 which also has an vaxial bore 36 the walls of which closely fit the outer face of post 13 and which has one major face 37 abutting the upper face of bi-metal blade 14 and another face 38 abutting ythe lower surface of terminal 22. The face 38 of bushing 35 has a cavity 39 coaxial with post 13 and conforming in shape and size to accommodate that portion of collar 29 protruding below the lower surface of terminal 22. Bushing 35 is shown in detail in FIG. 3.

Blade 16 and terminal 21 are spaced from blade 19 and terminal 22 by the major body portion of bushing 31. One major face 41 of that body portion abuts the upper surface of blade 19 and a second major face 42 abuts the lower surface of terminal 21 such that the spacing between those major faces deines the spacing of blade 19 and terminal 21.

The blade 15 and terminal 21 are spaced from support blade 25 by a second bushing 43 having major faces spaced to space the blade 16 from the blade 2S. A collar 44 corresponding to collar 29 extends through suitable apertures 45 and 46 in tbe terminal 2i and blade 16 respectively to maintain those blades coaxial with the post 13. Collar 44 lits into a socket or cavity 47 in bushing 31 of a shape and size to accommodate that portion of the `collar which protrudes below the lower surface of terminal 21. v l p in operation, the thermostatic switch functions in a conventional manneizTha't is, blades 16 and 19 are flexible'and 'can be displaced relative to the stack by the application of pressure on the upper surface 16 from pin 23 or the application of pressure on the lower surface of blade 16 from pin 15. Bimetallic blade 14 is responsive to temperature changes and ilexes in a conventional manner to carry the pin 15 toward and away from the blade 16 in accordance with changes in temperature. The ilexible blade 19 is provided with an upward set to insure that when the axis of post 13 is vertical and blade 16 horizontal, contact 13 will engage contact 17 and complete a circuit through the switch. Blade 16 is also provided with an upward set whereby the retreat of pin 23 under the influence of the adjustment of screw 25 permits the blade to move upward and separate contact 17 from contact 18.

Minimum over surface spacing between blades is provided by the depth of the major body portion of the bushings 35, 31 and 43. That is, the faces 37 and 38 of bushing 35 are spaced at least the minimum over surface spacing as are faces 41 and 42 of bushing 31.

In the above-described construction, the perimeter of the circular apertures in the terminals 21 and 22 and the blades 16 and 19 is spaced from the outer surface of the right circular cylindrical post 13 less than the minimum over surface spacing required for the voltages for which the switch structure is rated in order to permit a more compact structure. This is accomplished while retaining the rating requirements of the various specifying agencies which establish standards for electrical equipment by utilizing spacing along a path parallel to the axis of post 13 in combination with that radial to the axis of that post to provide the requisite over the surface spacing. The radial dimension is determined by the thickness of the right circular cylinder comprising the Wall of collar 29 and can also be defined by the difference in the radius of the outer dimension f the collar 29 and the outer dimension of the pin 13. This radial difference is less than,

the minimum spacing and additional spacing is provided by the cylindrical outer surface on the collar 29 which projects beyond the ringlike portion of the blade or terminal most proximate the free end of the collar. Thus in the case of bushing 31, which provides the spacing between post 13 and the terminal 22 and blade 19, the over surface spacing provided by the face 48 as best seen in FIG. 2, is less than the minimum over surface spacing required for the rating of the switch and the remaining portion of that spacing is made up by that portion of the cylindrical surface of collar 29 extending along the axis of the bushing from the intersection of that cylindrical surface with the annular face 48 to the surface of terminal 22 most proximate that intersection. It is the sum of this radial and longitudinal spacing that must equal the minimum over surface spacing requirement in order to make the switch acceptable for use in most approved appliances.

As an augmenting feature for the over surface spacing requirement, the cavity into which the protruding collar extends complements that collar by being at least deep enough to accommodate the protruding portion thereof. Thus as shown in FIG. 2 the depth of the cavity 47 in the major face 42 of the bushing can be less than the height of the collar 29 by an amount equal to the total thickness of the blade and terminal to be accommodated on the collar of the next adjacent bushing in the stack. I'n practice the cavity is somewhat deeper than this in order to avoid imposing compression on the collars of stacked bushings and to permit those compressive forces to be imposed upon the greater surface area afforded by the major faces of the bushing normal to its axis.

It is recognized that switch stacks bearing a superficial resemblance to those portrayed in FIG. l exist in the prior art. For example, in A. T. Smith Patent 2,190,276 of Feb. 13, 1940, for a Temperature Control for Electric Cooking Devices, a structure is shown including insulating bushings assembled on a center post and having collars which extend through circular apertures in contact blades and beyond the surfaces of those contact blades to fit into complementary cavities in the next adjacent bushing. However, no prior art is known wherein it has been appreciated that the dimensions of such stacks can be reduced by utilizing a portion of a collar surface extending parallel to the axis of the support post as a part of the spacing surface and thereby reducing the radial dimension through the thickness of the collar wall to less than the minimum over surface spacing required of the device. The reduction of the collar wall thickness to less than the minimum over surface spacing and the augmenting of the over surface spacing thus provided by sufficient spacing parallel to the axis of the bushing and mounting post to in total meet the minimum has provided a structure of smaller dimensions which has been accepted by the industry and is currently entering into large volume production for utilization in areas and at ratings heretofore unavailable for stacked switches of this type.

Having described the invention, I claim:

1. In combination a switch stack having a given rated operating voltage which requires a given minimum over surface spacing between conductive elements of different voltage levels comprising a conductive post, an insulating bushing embracing a portion of the length of said post, a collar extending from said first bushing along the length of said post, a conductive ring mounted on said collar, said collar having a wall thickness providing the requisite dielectric strength through said wall and spacing said ring and post less than said minimum over surface spacing, said collar having a length along said post extending beyond said ring a distance at least equal to the difference between said minimum over surface spacing and said collar thickness whereby said switch stack width can be reduced by utilizing over surface spacing radial and longitudinal of said post.

2. A combination according to claim 1 including a second insulating bushing embracing a portion of the length of said post, said second bushing having a major face abutting said ring, said major face having a cavity conforming to and receiving that portion of said collar extending beyond said ring.

3. A combination according to claim 1 wherein said post and said bushing are of circular cross section, and said aperture is circular whereby said collar thickness is essentially the dierence between the radius of said aperture and the radius of said post.

4. A combination according to claim 2 including a second conductive ring which in at least one operating condition of said switch is electrically isolated from said first mentioned conductive ring, said second insulating bushing having a major body portion of a thickness at least equal to said minimum over surface spacing and a collar protruding from the face of said major body portion opposite that major face having said cavity, said last mentioned collar coaxially spacing said second ring from said post and having a wall thickness less than said minimum over surface spacing, said last mentioned collar having a length along the axis of said post and beyond the face of said second ring most remote from said second bushing major body portion a distance at least equal to the difference between said minimum over surface spacing and said collar thickness.

5. A combination according to claim l whcrcin said insulating bushing hun gcnernlly parallel major faces normal to the longitudinal axis of said post and spaced at least said minimum over surface spacing, said collar extending from a iirst of said faces, and said face opposite said iirst face having a cavity of the form of said collar, said combination including n Second insulating bushing of the same geometry as said first mentioned bushing embracing n portion of thc length of said post and having its collar tclcscopically littcd within said cavity of said first bushing, and a second conductive ring mounted 0n the collar of said second bushing.

No references cited.

BERNARD A. GILHEANY, Primary Exmnz'fzer.

G. HARRIS, Assistant Examiner. 

1. IN COMBINATION A SWITCH STACK HAVING A GIVEN RATED OPERATING VOLTAGE WHICH REQUIRES A GIVEN MINIMUM "OVER SURFACE" SPACING BETWEEN CONDUCTIVE ELEMENTS OF DIFFERENT VOLTAGE LEVELS COMPRISING A CONDUCTIVE POST, AN INSULATING BUSHING EMBRACING A PORTION OF THE LENGTH OF SAID POST, A COLLAR EXTENDING FROM SAID FIRST BUSHING ALONG THE LENGTH OF SAID POST, A CONDUCTIVE RING MOUNTED ON SAID COLLAR, SAID COLLAR HAVING A WALL THICKNESS PROVIDING THE REQUISITE DIELECTRIC STRENGTH THROUGH SAID WALL AND SPACING SAID RING AND POST LESS THAN SAID MINIMUM "OVER SURFACE" SPACING, SAID COLLAR HAVING A LENGTH ALONG SAID POST EXTENDING BEYOND SAID RING A DISTANCE AT LEAST EQUAL TO THE DIFFERENCE BETWEEN SAID MINIMUM "OVER SURFACE" SPACING AND SAID COLLAR THICKNESS WHEREBY SAID SWITCH STACK WIDTH CAN BE REDUCED BY UTILIZING "OVER SURFACE" SPACING RADIAL AND LONGITUDINAL OF SAID POST. 